The present invention relates to a magnetic recording medium used for recording information on its magnetic film and a method of manufacturing such a recording medium. More particularly, the present invention relates to a magnetic recording medium having a continuous magnetic film on its surface and a method of manufacturing such a recording medium.
A conventional magnetic recording medium, such as a conventional magnetic disk used in an information recording and reproducing apparatus, is made by binding powder of an oxide magnetic material by an organic binder and coating a film of the oxide magnetic material on a surface of a base. Such a conventional magnetic recording medium will be referred to hereinafter as a coated type recording medium. With the ever-increasing demand for improvements in the recording density of such a coated type recording medium, a magnetic recording medium having a continuous thin film of a magnetic material on a surface of its base has been proposed to replace the coated type recording medium. The proposed recording medium will be referred to hereinafter as a thin-film type recording medium. The recording surface of the thin-film type recording medium is generally very flat and smooth, and, in order to prevent damage due to repeated relative sliding contact between a magnetic head and the recording surface, a lubricating agent is coated on the recording surface of the thin-film type recording medium. However, when the magnetic head stops its movement relative to the recording surface of the magnetic disk, a strong adhesion occurs between the head and the disk due to the presence of the lubricating agent on the recording surface. Therefore, when the relative movement is then to be started, a very large force is required to release the magnetic head from adhesion to the surface of the magnetic disk, with the result that the spring system supporting the magnetic head may be damaged, thereby giving rise to great operational troubles. Even in the absence of the lubricating agent, a phenomenon similar to the adhesion phenomenon described above may be caused by the presence of, for example, adsorbed moisture. Therefore, the undesirable adhesion should be avoided or prevented.
JP-A-57-20925 describes an invention in which, in order to prevent the undesirable adhesion described above, powder of a non-magnetic material is dispersed on the surface of a magnetic film provided on a base of a magnetic disk so as to form dispersed projections on the recording surface of the magnetic disk.
Also, JP-A-60-40528 and JP-A-60-136920 describe inventions in which fine powder of a hard non-magnetic magerial such as alumina is previously partly embedded under pressure in a surface of a base of a magnetic disk so as to form dispersed projections on the recording surface of a magnetic film of the magnetic disk. In each of these inventions, no adhesion between a magnetic head and the magnetic disk occurs, because the magnetic head brought into sliding contact with the magnetic film does not make direct intimate contact with the magnetic film due to the presence of the projections.
However, the stability of the projections is not taken into consideration in the disclosure of JP-A-57-20925 cited above. More precisely, how to attach the non-magnetic powder to the surface of the magnetic film is not specifically described in JP-A-57-20925 cited above, and the results of an experiment conducted by the inventors to attach powder of alumina to the surface of the magnetic film by such a means as a binder have proved that the powder of alumina tends to be easily detached from the surface.
The stability of the projections is not also taken into consideration in the disclosure of each of JP-A-60-40528 and JP-A-60-136920 cited above, and there has been such a problem that, during cleaning the base, the projections are partly detached thereby leaving pit-like defects.